scholarly journals Magneto-active elastic shells with tunable buckling strength

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Dong Yan ◽  
Matteo Pezzulla ◽  
Lilian Cruveiller ◽  
Arefeh Abbasi ◽  
Pedro M. Reis
Keyword(s):  
Functional Materials ◽  
Underlying Mechanism ◽  
Magnetic Actuation ◽  
Engineering Structures ◽  
Governing Parameter ◽  
Elastic Shells ◽  
Buckling Strength ◽  
Shell Buckling ◽  
Theoretical Predictions ◽  
Extreme Sensitivity

AbstractShell buckling is central in many biological structures and advanced functional materials, even if, traditionally, this elastic instability has been regarded as a catastrophic phenomenon to be avoided for engineering structures. Either way, predicting critical buckling conditions remains a long-standing challenge. The subcritical nature of shell buckling imparts extreme sensitivity to material and geometric imperfections. Consequently, measured critical loads are inevitably lower than classic theoretical predictions. Here, we present a robust mechanism to dynamically tune the buckling strength of shells, exploiting the coupling between mechanics and magnetism. Our experiments on pressurized spherical shells made of a hard-magnetic elastomer demonstrate the tunability of their buckling pressure via magnetic actuation. We develop a theoretical model for thin magnetic elastic shells, which rationalizes the underlying mechanism, in excellent agreement with experiments. A dimensionless magneto-elastic buckling number is recognized as the key governing parameter, combining the geometric, mechanical, and magnetic properties of the system.

scholarly journals A Ternary Map of Ni–Mn–Ga Heusler Alloys from Ab Initio Calculations

Metals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 973
Author(s):  
Yulia Sokolovskaya ◽  
Olga Miroshkina ◽  
Danil Baigutlin ◽  
Vladimir Sokolovskiy ◽  
Mikhail Zagrebin ◽  
...  
Keyword(s):  
First Principles ◽  
Predictive Power ◽  
Computational Study ◽  
Heusler Alloys ◽  
Functional Materials ◽  
Ternary Diagram ◽  
Compositional Stability ◽  
Theoretical Predictions ◽  
Simultaneous Stability ◽  
Tetragonal Martensite

In the search for new magnetic functional materials, non-stoichiometric compounds remain a relatively unexplored territory. While experimentalists create new compositions looking for improved functional properties, their work is not guided by systematic theoretical predictions. Being designed for perfect periodic crystals, the majority of first-principles approaches struggle with the concept of a non-stoichiometric system. In this work, we attempt a systematic computational study of magnetic and structural properties of Ni–Mn–Ga, mapped onto ternary composition diagrams. Compositional stability was examined using the convex hull analysis. We show that the cubic austenite has its stability region close to the stoichiometric Ni2MnGa, in agreement with experimental data, while the tetragonal martensite spreads its stability over a wider range of Mn and Ni contents. The unstable compositions in both austenite and martensite states are located in the Ga-rich corner of the ternary diagram. We note that simultaneous stability of the austenite and martensite should be considered for potentially stable compounds suitable for synthesis. The majority of compounds are predicted to be ferrimagnetically ordered in both austenitic and martensitic states. The methodology used in this work is computationally tractable, yet it delivers some predictive power. For experimentalists who plan to synthesize stable Ni–Mn–Ga compounds with ferromagnetic order, we narrow the target compositional range substantially.

Buckling of Thin Cylindrical Shells Under Locally Elevated Compressive Stresses

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
J. Michael Rotter ◽  
Minjie Cai ◽  
J. Mark F. G. Holst
Keyword(s):  
Stress State ◽  
Cylindrical Shells ◽  
Peak Stress ◽  
Theoretical Research ◽  
Design Rule ◽  
Uniform Stress ◽  
Geometric Imperfection ◽  
Buckling Strength ◽  
Shell Buckling ◽  
Compressive Stresses

Thin cylindrical shells used in engineering applications are often susceptible to failure by elastic buckling. Most experimental and theoretical research on shell buckling relates only to simple and relatively uniform stress states, but many practical load cases involve stresses that vary significantly throughout the structure. The buckling strength of an imperfect shell under relatively uniform compressive stresses is often much lower than that under locally high stresses, so the lack of information and the need for conservatism have led standards and guides to indicate that the designer should use the buckling stress for a uniform stress state even when the peak stress is rather local. However, this concept leads to the use of much thicker walls than is necessary to resist buckling, so many knowledgeable designers use very simple ideas to produce safe but unverified designs. Unfortunately, very few scientific studies of shell buckling under locally elevated compressive stresses have ever been undertaken. The most critical case is that of the cylinder in which locally high axial compressive stresses develop extending over an area that may be comparable with the characteristic size of a buckle. This paper explores the buckling strength of an elastic cylinder in which a locally high axial membrane stress state is produced far from the boundaries (which can elevate the buckling strength further) and adjacent to a serious geometric imperfection. Care is taken to ensure that the stress state is as simple as possible, with local bending and the effects of internal pressurization eliminated. The study includes explorations of different geometries, different localizations of the loading, and different imperfection amplitudes. The results show an interesting distinction between narrower and wider zones of elevated stresses. The study is a necessary precursor to the development of a complete design rule for shell buckling strength under conditions of locally varying axial compressive stress.

scholarly journals Kinetic Control over Droplet Ripening in Fuel-Driven Active Emulsions

2020 ◽  
Author(s):  
Marta Tena-Solsona ◽  
Jacqueline Janssen ◽  
Caren Wanzke ◽  
Fabian Schnitter ◽  
Hansol Park ◽  
...  
Keyword(s):  
Collective Behavior ◽  
Ostwald Ripening ◽  
Underlying Mechanism ◽  
Droplet Growth ◽  
Metabolic Reaction ◽  
Reaction Cycle ◽  
Experimental Systems ◽  
Theoretical Predictions ◽  
Chemical Cycle ◽  
Kinetics Of

Active droplets are made of phase-separated molecules that are activated and deactivated by a metabolic reaction cycle. Such droplets play a crucial role in biology as a class of membrane-less organelles. Moreover, theoretical studies show that active droplets can evolve to the same size or spontaneously self-divide when energy is abundant. All of these exciting properties, i.e., emergence, decay, collective behavior, and self-division, are pivotal to the functioning of life. However, these theoretical predictions lack experimental systems to test them quantitively. Here, we describe the synthesis of synthetic active droplets driven by a metabolic chemical cycle and we find a surprising new behavior, i.e., the dynamics of droplet-growth is regulated by the kinetics of the fuel-driven reaction cycle. Consequently, these droplets ripen orders of magnitude faster compared to Ostwald ripening. Combining experiments and theory, we elucidate the underlying mechanism, which could help better understand how cells regulate the growth of membrane-less organelles.<br>

scholarly journals Unveiling the Key Templates in the Self-Assembly of Gigantic Molybdenum Blue Wheels

2018 ◽  
Author(s):  
Weimin Xuan ◽  
Robert Pow ◽  
Qi Zheng, ◽  
Nancy Watfa ◽  
De-Liang Long ◽  
...  
Keyword(s):  
Self Assembly ◽  
Electrostatic Interactions ◽  
Structural Evolution ◽  
Functional Materials ◽  
Building Blocks ◽  
Underlying Mechanism ◽  
The Self ◽  
Supramolecular Systems ◽  
Structure Directing Agent ◽  
Molybdenum Blue

Template synthesis is a powerful and useful approach to build a variety of functional materials and complicated supramolecular systems. Systematic study on how templates structurally evolve from basic building blocks and then affect the templated self-assembly is critical to understand the underlying mechanism and gain more guidance for designed assembly but remains challenging. Here we describe the templated self-assembly of a series of gigantic Mo Blue (MB) clusters 1-4 using L-ornithine as structure-directing agent. L-ornithine is essential for the formation of such kind of template⊂host assemblies by providing directional forces of hydrogen bonding and electrostatic interactions. Based on the structural relationship between encapsulated templates of {Mo8} (1), {Mo17} (2) and {Mo36} (4), a plausible pathway of the structural evolution of templates is proposed, thus giving more insight on the templated self-assembly of Mo Blue clusters.

scholarly journals Unified Theory for Hybrid-Photocatalysts: A Review on New Strategies for Synergic, Enhanced Conversion Efficacy and Photoredox Cycle

2021 ◽  
Author(s):  
Jui-Teng Lin
Keyword(s):  
Steady State ◽  
Light Intensity ◽  
Polymer Network ◽  
Transient State ◽  
Functional Materials ◽  
State Dependence ◽  
Comprehensive Model ◽  
Effective Absorption Coefficient ◽  
Theoretical Predictions ◽  
Reported Data

This article presents, for the first time, comprehensive model based on the proposed mechanism of Rahal et al [17], Bonardi {20], Tar et al [20], and Mau et al [24], for 3-component systems of G1/Iod/EDB, G1/Iod/amine (in gold chloride), and Iod/Benzoic/Borate (for reduced oxygen inhibition) for the hybri free radical (FRP) and cationic (CP) photopolymerization of interpenetrated polymer network (IPN) systems. Analytic formulas are developed to explore the new features including: (i) conversion efficacy(CE) of FRP is an increasing function of the light intensity (I), the effective absorption coefficient (b), for transient state, whereas, CE at steady-state is independent to the light intensity; (ii) initiator regeneration (RGE)
provides a catalytic cycle for improved CE for FRP and CP; (iii) in the IPN system, the synergic effects due to the co-exist of FRP and CP include: (i) CP can increase the medium viscosity limiting the diffusional oxygen replenishment, such that OIH is reduced; (ii) the cationic monomer also acts as a diluting agent for the radical polymer network, and (iii) the exothermic property of the CP polymerization. We have proposed ascaling law for the transient and steady-state dependence of CE on the key parameter P=bIC0, given by a an m-order power law of Pm, with m = 0.5 to 1.5, depending on various conditions. The CE also has an optimal value for maximum CE. The presented comprehensive model (with minimum mathematics) focusing on the enhancement mechanisms/pathways, provides analytic formulas which can be used to analyze reported data, and, more importantly, serves as guidance for exploring new functional materials or new kinetic schemes for improved conversion or procedures for both industrial and medical applications such as additive manufacturing (AM), 3D and 4D bioprinting. Finally, we have proposed new directions/experiments based on our theoretical predictions.

Microstructure of Grain Boundary Junctions in Bicrystal High-Tc Superconductor SQUIDs and its Relation with the Device Noise

1997 ◽  
Vol 3 (S2) ◽  
pp. 667-668
Author(s):  
Y. Huang ◽  
L. Lee ◽  
M. Teepe ◽  
K. L. Merkle ◽  
K. Char
Keyword(s):  
Grain Boundary ◽  
Quantum Interference ◽  
Underlying Mechanism ◽  
Low Noise ◽  
Noise Performance ◽  
Ion Milling ◽  
High Tc ◽  
Ybco Films ◽  
Extreme Sensitivity ◽  
Non Destructive

Superconductor Quantum Interference Devices (SQUIDs), because of their extreme sensitivity to magnetic fields and radiation, have found important applications in biomagnetism, non-destructive evaluation and geophysics. One problem in the application of high-Tc SQUIDs is their noise performance. Recently, considerable progress has been made in reducing the noise. To understand the underlying mechanism, it is important to identify the microstructural origin of the junction noise.In this work actual SQUIDs of good and poor noise performance are studied and compared by TEM. The devices were made by epitaxially growing YBa2Cu3O7-x (YBCO) films using laser ablation on 24° SrTiO3 bi-crystal substrates. The TEM samples were prepared by polishing and ion milling. The TEM observation was performed on a JEOL EM-4000EXII and a Hitachi H-9000 microscope.Observation shows that the YBCO films and the grain boundary junctions (GB J) in the low-noise devices are in good quality. The microstructure of the films and the boundaries in the films are shown in fig. 1 and 2.

scholarly journals Giant field-induced strains in magnetoactive elastomer composites

2013 ◽  
Vol 469 (2158) ◽  
pp. 20130385 ◽  
Author(s):  
E. Galipeau ◽  
P. Ponte Castañeda
Keyword(s):  
Exact Analytical Solution ◽  
Functional Materials ◽  
New Class ◽  
Small Strains ◽  
Magnetic Layers ◽  
Field Dependent ◽  
Theoretical Predictions ◽  
Strong Action ◽  
Elastomer Composites ◽  
Magnetoactive Elastomer

Magnetoactive elastomers (MAEs) are composite materials consisting of nearly rigid, magnetically susceptible particles embedded in a soft, magnetically insensitive elastomer matrix. These multi-functional materials exhibit field-dependent strains and changes in stiffness. However, the strains that have been achieved experimentally to date are still relatively small (of the order of 1%). The reason for these small strains can be traced back to the dipolar nature of the forces between particles. Large particle concentrations are required to generate strong forces, but large concentrations also lead to large overall stiffness for the composite material, which, in turn, tends to reduce the overall strain. In this paper, we propose a new class of MAEs with doubly layered, herringbone-type microstructures capable of generating much larger field-induced strains of up to 100%. This is accomplished by combining the strong action of magnetic torques on suitably oriented magnetic layers, which interact directly with the applied magnetic field, together with the excitation of soft modes of simple shear deformation in the elastomer layers. Theoretical predictions, based on an exact analytical solution for the macroscopic magnetoelastic response of the materials, allow for the optimization of the microstructure for enhanced magnetostriction.

Buckling of Externally Pressurized Composite Torispherical Domes

1989 ◽  
Vol 203 (1) ◽  
pp. 41-56 ◽  
Author(s):  
G D Galletly ◽  
A Muc
Keyword(s):  
Shear Modulus ◽  
Failure Mode ◽  
Young Modulus ◽  
External Pressure ◽  
Limited Extent ◽  
Woven Composite ◽  
Plane Shear ◽  
Buckling Strength ◽  
Shell Buckling ◽  
Theory And Experiment

The results of external pressure buckling tests on 0.25 m diameter woven composite (mainly CFRP) domes are given in the paper and they are compared with the predictions of the shell buckling program BOSOR 4. The agreement between theory and experiment was satisfactory. The tests also show that the buckling strength of CFRP torispheres is good. They could replace steel torispheres and would be considerably lighter. The buckling pressures of the woven composite domes are a function of the Young modulus E but the relation is not a simple linear one (the in-plane shear modulus G12 also needs to be taken into account). Results of some tests on CFRP and GFRP domes lend support to this statement. The provisions of BS 4994, when applied to these domes, predict that buckling is the controlling failure mode. While this is correct, the buckling pressures predicted by BS 4994 seem rather low. The effect of dome thickness on the buckling pressures was expected to vary as (t/R)2. This was confirmed herein, to a limited extent, by a few tests on shallow CFRP domes.

scholarly journals Inevitability and containment of replication errors for eukaryotic genome lengths spanning megabase to gigabase

2016 ◽  
Vol 113 (39) ◽  
pp. E5765-E5774 ◽  
Author(s):  
Mohammed Al Mamun ◽  
Luca Albergante ◽  
Alberto Moreno ◽  
James T. Carrington ◽  
J. Julian Blow ◽  
...  
Keyword(s):  
Entire Range ◽  
Error Rates ◽  
Replication Forks ◽  
Replication Error ◽  
Replication Errors ◽  
Middle Domain ◽  
Theoretical Predictions ◽  
Extreme Sensitivity ◽  
The Mean ◽  
Great Simplicity

The replication of DNA is initiated at particular sites on the genome called replication origins (ROs). Understanding the constraints that regulate the distribution of ROs across different organisms is fundamental for quantifying the degree of replication errors and their downstream consequences. Using a simple probabilistic model, we generate a set of predictions on the extreme sensitivity of error rates to the distribution of ROs, and how this distribution must therefore be tuned for genomes of vastly different sizes. As genome size changes from megabases to gigabases, we predict that regularity of RO spacing is lost, that large gaps between ROs dominate error rates but are heavily constrained by the mean stalling distance of replication forks, and that, for genomes spanning ∼100 megabases to ∼10 gigabases, errors become increasingly inevitable but their number remains very small (three or less). Our theory predicts that the number of errors becomes significantly higher for genome sizes greater than ∼10 gigabases. We test these predictions against datasets in yeast, Arabidopsis, Drosophila, and human, and also through direct experimentation on two different human cell lines. Agreement of theoretical predictions with experiment and datasets is found in all cases, resulting in a picture of great simplicity, whereby the density and positioning of ROs explain the replication error rates for the entire range of eukaryotes for which data are available. The theory highlights three domains of error rates: negligible (yeast), tolerable (metazoan), and high (some plants), with the human genome at the extreme end of the middle domain.

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